Spalling with laser-defined spall edge regions

ABSTRACT

Laser ablation can be used to form a trench within at least a blanket layer of a stressor layer that is atop a base substrate. A non-ablated portion of the stressor layer has an edge that defines the edge of the material layer region to be spalled. Laser ablation can also be used to form a trench within a blanket material stack including at least a plating seed layer. A stressor layer is formed on the non-ablated portions of the material stack and one portion of the stressor layer has an edge that defines the edge of the material layer region to be spalled. Laser ablation can be further used to form a trench that extends through a blanket stressor layer and into the base substrate itself. The trench has an edge that defines the edge of the material layer region to be spalled.

BACKGROUND

The present disclosure relates to semiconductor device manufacturing,and more particularly, to methods for spalling, i.e., removing, amaterial layer region of a base substrate, wherein laser ablation isused to define an edge of the material layer region that is to bespalled.

Devices that can be produced in thin-film form have three clearadvantages over their bulk counterparts. First, by virtue of lessmaterial used, thin-film devices ameliorate the materials costassociated with device production. Second, low device weight is adefinite advantage that motivates industrial-level effort for a widerange of thin-film applications. Third, if dimensions are small enough,devices can exhibit mechanical flexibility in their thin-film form.Furthermore, if the substrate from which a device layer is removed canbe reused, additional fabrication cost reduction can be achieved.

Recent advances in spalling techniques now make it possible to remove,i.e., spall, a thin (typically less than 100 μm) semiconductor layerfrom an entire surface of base semiconductor substrate with near-zerothickness direction kerf losses, and to do this multiple times on thesame base semiconductor substrate. The potential cost savings areenormous since (i) the thickness of the spalled semiconductor layer canbe limited to the thickness needed for thin-film devices and (ii) manysemiconductor layers may be derived from a single base substrate.

U.S. Patent Application Publication No. 2010/0311250 to Bedell et al.discloses a spalling process that can be employed in removing a thinsemiconductor device layer from a base semiconductor substrate. Thespalling method disclosed in the aforementioned publication includesdepositing a stressor layer (i.e., a spall-inducing layer) on a basesemiconductor substrate, placing an optional handle substrate on thestressor layer, and inducing a crack and its propagation below thesubstrate/stressor interface. This process, which is performed at roomtemperature, removes a thin layer of the base semiconductor substratebelow the stressor layer. As some stages after spalling, some or all ofthe stressor layer can be removed utilizing an etch process.

Further improvements of spalling are needed which render spalling moreefficient, controllable, and economical and thus more reliable for usein forming thin film devices.

SUMMARY

Laser ablation is used for defining an edge of a material layer region(or portion) that is to be removed from a spalling structure comprisingat least a base substrate and a stressor layer. In one embodiment, laserablation is used to form a trench within at least a blanket layer of astressor layer that is located atop a base substrate. A non-ablatedportion of the stressor layer has an edge that defines the edge of thematerial layer region to be spalled. In another embodiment, laserablation is used to form a trench within a blanket material stackincluding at least a plating seed layer. A stressor layer is formed onthe non-ablated portions of the material stack and one portion of thestressor layer has an edge that defines the edge of the material layerregion to be spalled. In another embodiment, laser ablation is used toform a trench that extends through a blanket stressor layer and into thebase substrate itself. The trench has an edge that defines the edge ofthe material layer region to be spalled.

In one embodiment of the present disclosure, a method of spalling, i.e.,removing, a material layer region (or portion) of a base substrate isprovided. The method includes forming at least a stressor layer atop anuppermost surface of a base substrate. A trench is formed by laserablation at least within the stressor layer to define an edge of amaterial layer region to be spalled. The material layer region of thebase substrate is then spalled.

In another embodiment of the present disclosure, another method ofspalling, i.e., removing, a material layer region (or portion) of a basesubstrate is provided. In this embodiment, the method includes forming amaterial stack comprising at least a plating seed layer atop anuppermost surface of a base substrate. A trench is formed by laserablation at least within the material stack to define an edge of amaterial layer region to be spalled. A stressor layer portion is thenformed on a non-ablated portion of the material stack. Next, thematerial layer region of the base substrate is spalled.

In a further embodiment of the present disclosure, a further method ofspalling, i.e., removing, a material layer region (or portion) of a basesubstrate is provided. In this embodiment, the method includes formingat least a stressor layer atop an uppermost surface of a base substrate.A trench is formed by laser ablation within a vertical sidewall portionof the base substrate. The trench defines an edge of a material layerregion of the base substrate to be spalled. The material layer region ofthe base substrate is then spalled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial representation (though a cross-sectional view)illustrating a base substrate that can be employed in one embodiment ofthe present disclosure.

FIG. 2 is a pictorial representation (though a cross sectional view)illustrating the base substrate after forming an optionalmetal-containing adhesion layer, an optional plating seed layer and astressor layer thereon.

FIG. 3A-3E are pictorial representations (through cross sectional views)illustrating the structure of FIG. 2 after forming a trench by laserablation; in FIG. 3A, the trench stops on an uppermost surface of thebase substrate, in FIG. 3B, the trench extends in the base substrate toa depth that is less than the fracture plane, in FIG. 3C, the trenchextends in the base substrate to a depth that is equal to the fractureplane, in FIG. 3D, the trench extends in the base substrate to a depththat is greater than the fracture plane depth, and, in FIG. 3E, thetrench extends in the base substrate and has an expanded width opening.

FIG. 4 is a pictorial representation (though a cross sectional view)illustrating the structure of FIG. 3A after forming an optional handlesubstrate atop the stressor layer.

FIG. 5 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 4 after removing a material layerregion of the base substrate by spalling.

FIG. 6 is a pictorial representation (through a cross sectional view)illustrating the base substrate of FIG. 1 after forming a material stackcomprising at least a plating seed layer.

FIG. 7 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 6 after forming a trench through thematerial stack and within a portion of the base substrate.

FIGS. 8A-8B are pictorial representations (through cross sectionalviews) illustrating the structure of FIG. 7 after forming a stressorlayer; in FIG. 8A the stressor layer is formed by selective plating,while in FIG. 8B the stressor layer is formed by non-selective plating.

FIG. 9 is a pictorial representation (though a cross sectional view)illustrating the structure of FIG. 8A after forming an optional handlesubstrate atop the stressor layer.

FIG. 10 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 9 after removing a material layerregion of the base substrate by spalling.

FIG. 11 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 2 after forming a laser-generatedtrench in a vertical sidewall of the base substrate.

FIG. 12 is a pictorial representation (though a cross sectional view)illustrating the structure of FIG. 11 after forming an optional handlesubstrate atop the stressor layer.

FIG. 13 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 12 after removing a material layerregion of the base substrate by spalling.

FIG. 14A-14D are pictorial representations (through top-down views)depicting representative examples of the different laser scribe patternsthat can be used in the present disclosure.

DETAILED DESCRIPTION

The present disclosure, which relates to methods of spalling a materiallayer region (or portion) from a base substrate using laser ablation todefine an edge of the material layer region to be spalled, will now bedescribed in greater detail by referring to the following discussion anddrawings that accompany the present application. It is noted that thedrawings of the present application are provided for illustrativepurposes and, as such, they are not drawn to scale.

In the following description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps and techniques, in order to provide a thoroughunderstanding of the present invention. However, it will be appreciatedby one of ordinary skill in the art that the present disclosure may bepracticed with viable alternative process options without these specificdetails. In other instances, well-known structures or processing stepshave not been described in detail in order to avoid obscuring thevarious embodiments of the present disclosure.

It will be understood that when an element as a layer, region, orsubstrate is referred to as being “on” or “over” another element, it canbe directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “beneath” or “under” another element, it can bedirectly beneath or under the other element, or intervening elements maybe present. In contrast, when an element is referred to as being“directly beneath” or “directly under” another element, there are nointervening elements present.

Despite being able to spall a thin semiconductor layer from a basesemiconductor substrate, there are some concerns with prior art spallingmethods. For example, the controlled spalling of the prior art is bestinitiated from a stressor layer that has an abrupt and sharply definededge profile (versus a tapered edge profile in which the stressor layerthickness gradually decreases to zero over a macroscopic distance).

For best results, the edge of the stressor layer is formed in proximityto a vertical sidewall of the underlying base substrate. In one approachto the stressor layer formation, the edges of stressor layer are alignedwith the outer edges of the base substrate. However, since perfectalignment can be difficult to achieve, some portion of the stressorlayer can extend onto the sidewalls of the base substrate, potentiallyinhibiting spalling. Alternatively, the stressor layer dimensions can bedesigned so that there is a border between the stressor layer edges andthe edge of the substrate. However, defining such a borderlithographically can add cost and complexity to the spalling process. Itwould therefore be beneficial to have a simple, non-lithographic processfor forming edges in a stressor layer.

There are also reasons to believe that stress concentrations favorablefor controlled spalling might result from changing the local geometry ofthe base substrate near the edge of the stressor layer. For example, onemight pattern a Ni stressor layer on a base substrate to form a Ni mesaregion with sharply defined edges and then recess some portion of theexposed base substrate immediately adjacent to the Ni edges to extendthe mesa structure into the base substrate. It would therefore bebeneficial to have a simple and inexpensive method for forming suchstructures.

Finally, large-area spalls are prone to cracking during spalling andsubsequent handling, while alternative approaches based on tilingmultiple small-area spalls present potential difficulties in keepingtrack of or handling multiple pieces. It would therefore be beneficialto have a method with the advantages of small pieces (i.e., less bendingand cracking) but the ease of single, large area pieces.

The above concerns are addressed in the present disclosure by employedlaser ablation for defining an edge within a material layer that can beused for spalling. By “laser ablation” it is meant a process in whichlaser irradiation is used to remove a material layer from a spallingstructure. By “spalling structure” it is meant a structure including atleast a base substrate and at least one material layer, e.g., stressorlayer and/or plating seed layer, formed thereon.

As described above, laser irradiation can be used to ablate, i.e.,remove material. In addition to removing material, laser irradiation canalso cause a local heating and/or a material redistribution that can beused in some embodiments to change the stress within the spallingstructure. For example, laser heating of the stressor layer stack edgesadjacent to the ablated trench may produce a grain growth in thestressor layer stack material that results in a change in stress at thestressor layer edge. The stress characteristics of the spallingstructure can also be altered by the redistributed trench material thatcan pile up on the stressor layer stack at the trench edges. Withoutwishing to be bound by any theory, it appears that liquid melt materialin the irradiated region trench region is driven out of the center ofthe trench area by the pressure of the vapor ablation plume, leaving theexpelled liquid to solidify on and above the trench edges. Suchlaser-induced alterations in stressor layer edge morphology and stresscan be exploited to tune the threshold stress required for spallinitiation.

In one embodiment, laser ablation is used to form a trench within atleast a blanket layer of a stressor layer that is located atop a basesubstrate. A remaining portion of the laser ablated stressor layer hasan edge that can be used for spalling. This embodiment of the presentdisclosure is illustrated in FIGS. 1, 2, 3A-3E, 4 and 5 of the presentdisclosure.

Referring first to FIG. 1, there is shown a base substrate 10 having anuppermost surface 12 that can be employed in one embodiment of thepresent disclosure. The base substrate 10 employed in the presentdisclosure may comprise a semiconductor material, a glass, a ceramic, orany another material whose fracture toughness is less than that of thestressor layer to be subsequently formed.

Fracture toughness is a property which describes the ability of amaterial containing a crack to resist fracture. Fracture toughness isdenoted K_(Ic). The subscript Ic denotes mode I crack opening under anormal tensile stress perpendicular to the crack, and c signifies thatit is a critical value. Mode I fracture toughness is typically the mostimportant value because spalling mode fracture usually occurs at alocation in the substrate where mode II stress (shearing) is zero, andmode III stress (tearing) is generally absent from the loadingconditions. Fracture toughness is a quantitative way of expressing amaterial's resistance to brittle fracture when a crack is present.

When the base substrate 10 comprises a semiconductor material, thesemiconductor material may include, but is not limited to Si, Ge, SiGe,SiGeC, SiC, Ge alloys, GaSb, GaP, GaAs, InAs, InP, and all other III-Vor II-VI compound semiconductors. In some embodiments, the basesubstrate 10 is a bulk semiconductor material. In other embodiments, thebase substrate 10 may comprise a layered semiconductor material such as,for example, a semiconductor-on-insulator or a semiconductor on apolymeric substrate. Illustrated examples of semiconductor-on-insulatorsubstrates that can be employed as base substrate 10 includesilicon-on-insulators and silicon-germanium-on-insulators.

When the base substrate 10 comprises a semiconductor material, thesemiconductor material can be doped, undoped or contain doped regionsand undoped regions.

In one embodiment, the semiconductor material that can be employed asthe base substrate 10 can be single crystalline (i.e., a material inwhich the crystal lattice of the entire sample is continuous andunbroken to the edges of the sample, with no grain boundaries). Inanother embodiment, the semiconductor material that can be employed asthe base substrate 10 can be a polycrystalline (i.e., a material that iscomposed of many crystallites of varying size and orientation; thevariation in direction can be random (called random texture) ordirected, possibly due to growth and processing conditions). In yetanother embodiment of the present disclosure, the semiconductor materialthat can be employed as the base substrate 10 can be amorphous (i.e., anon-crystalline material that lacks the long-range order characteristicof a crystal). Typically, the semiconductor material that can beemployed as the base substrate 10 is a single crystalline material.

When the base substrate 10 comprises a glass, the glass can be aSiO₂-based glass which may be undoped or doped with an appropriatedopant. Examples of doped SiO₂-based glasses that can be employed as thebase substrate 10 include undoped silicate glass, borosilicate glass,phosphosilicate glass, fluorosilicate glass, and borophosphosilicateglass.

When the base substrate 10 comprises a ceramic, the ceramic is anyinorganic, non-metallic solid such as, for example, an oxide including,but not limited to, alumina, beryllia, ceria and zirconia, a non-oxideincluding, but not limited to, a carbide, a boride, a nitride or asilicide; or composites that include combinations of oxides andnon-oxides.

In some embodiments of the present disclosure, one or more devicesincluding, but not limited to, transistors, capacitors, diodes, BiCMOS,resistors, etc. can be processed on and/or within the uppermost surface12 of the base substrate 10 utilizing techniques well known to thoseskilled in the art.

In some embodiments of the present disclosure, the uppermost surface 12of the base substrate 10 can be cleaned prior to further processing toremove surface oxides and/or other contaminants therefrom. In oneembodiment of the present disclosure, the base substrate 10 is cleanedby applying to the base substrate 10 a solvent such as, for example,acetone and isopropanol, which is capable of removing contaminatesand/or surface oxides from the uppermost surface 12 of the basesubstrate 10.

Referring to FIG. 2, there is depicted the base substrate 10 of FIG. 1after forming an optional metal-containing adhesion layer 14, anoptional plating seed layer 15, and a stressor layer 16 atop theuppermost surface 12 of the base substrate 10. In some embodiments, atleast one of the optional metal-containing adhesion layer 14 and theoptional plating seed layer 15 is employed. In other embodiments, boththe optional metal-containing adhesion layer 14 and the optional platingseed layer 15 are employed.

The optional metal-containing adhesion layer 14 is employed inembodiments in which the stressor layer to be subsequently formed haspoor adhesion to uppermost surface 12 of base substrate 10. Typically,the metal-containing adhesion layer 14 is employed when ametal-containing stressor layer is employed.

The optional metal-containing adhesion layer 14 employed in the presentdisclosure includes any metal adhesion material such as, but not limitedto Ti/W, Ti, Cr, Ni or any combination thereof. The optionalmetal-containing adhesion layer 14 may comprise a single layer or it mayinclude a multilayered structure comprising at least two layers ofdifferent metal adhesion materials.

The metal-containing adhesion layer 14 that can be optionally formed onthe uppermost surface 12 of base substrate 12 can be formed at roomtemperature (15° C.-40° C.) or above. In one embodiment, the optionalmetal-containing adhesion layer 14 can be formed at a temperature whichis from 20° C. to 180° C. In another embodiment, the optionalmetal-containing adhesion layer 14 can be formed at a temperature whichis from 20° C. to 60° C.

The metal-containing adhesion layer 14, which may be optionallyemployed, can be formed utilizing deposition techniques that are wellknown to those skilled in the art. For example, the optionalmetal-containing adhesion layer 14 can be formed by sputtering, chemicalvapor deposition, plasma enhanced chemical vapor deposition, chemicalsolution deposition, physical vapor deposition, and plating. Whensputter deposition is employed, the sputter deposition process mayfurther include an in-situ sputter clean process before the deposition.

When employed, the optional metal-containing adhesion layer 14 typicallyhas a thickness of from 5 nm to 200 nm, with a thickness of from 50 nmto 150 nm being more typical. Other thicknesses for the optionalmetal-containing adhesion layer 14 that are below and/or above theaforementioned thickness ranges can also be employed in the presentdisclosure.

The optional plating seed layer 15 is employed in embodiments in whichthe stressor layer to be subsequently formed is a metal and plating isused to form the metal-containing stressor layer. The optional platingseed layer 15 is employed to selectively promote subsequent plating of apre-selected metal-containing stressor layer. The optional plating seedlayer 15 may comprise, for example, single layer of Ni or a layeredstructure of two or more metals such as Al(bottom)/Ti/Ni(top).

The thickness of the optional seed layer 15 may vary depending on thematerial or materials of the optional plating seed layer 15 as well asthe technique used in forming the same. Typically, the optional platingseed layer 15 has a thickness from 2 nm to 400 nm. The optional platingseed layer 15 can be formed by a conventional deposition processincluding, for example, chemical vapor deposition (CVD), plasma-enhancedchemical vapor deposition (PECVD), atomic layer deposition (ALD), andphysical vapor deposition (PVD) techniques that may include evaporationand/or sputtering.

In one embodiment in which the optional metal-containing adhesion layer14 is employed, the stressor layer 16 can be formed directly on an uppersurface of the optional metal-containing adhesion layer 14. In someembodiments, the stressor layer 16 can be formed directly on an uppersurface of the optional plating seed layer 15. In some embodiments inwhich the optional metal-containing adhesion layer 14 and the optionalplating seed layer 15 are not present, the stressor layer 16 is formeddirectly on the upper surface 12 of base substrate 10; this particularembodiment is not shown in the drawings, but can readily be deduced fromthe drawings illustrated in the present application.

The stressor layer 16 employed in the present disclosure includes anymaterial that is under tensile stress on base substrate 10 at thespalling temperature. As such, the stressor layer 16 can also bereferred to herein as a stress-inducing layer. In accordance with thepresent disclosure, the stressor layer 16 has a critical thickness andstress value that cause spalling mode fracture to occur within the basesubstrate 10. By “spalling mode fracture” it is meant that a crack isformed within base substrate 10 and the combination of loading forcesmaintain a crack trajectory at a depth below the stressor/substrateinterface. By critical condition, it is meant that for a given stressormaterial and base substrate material combination, a thickness value anda stressor value for the stressor layer is chosen that render spallingmode fracture possible (can produce a K_(I) value greater than theK_(IC) of the substrate).

In the drawings, the dotted line that is designated as element 18represent the fracture plane or spalling depth. The fracture plane 18 isnominally parallel to upper surface 12 of base substrate 10. The terms“spalling depth” and “fracture plane” are used interchangeably anddefined as the vertical spacing between doted line 18 and the uppersurface 12 of base substrate 10.

The thickness of the stressor layer 16 is chosen to provide the desiredfracture depth within the base substrate 10. For example, if thestressor layer 16 is chosen to be Ni, then fracture will occur at adepth below the stressor layer 16 roughly 2 to 3 times the Ni thickness.The stress value for the stressor layer 16 is then chosen to satisfy thecritical condition for spalling mode fracture. This can be estimated byinverting the empirical equation given by t*=[(2.5×10⁶) (K_(IC)^(3/2))]/σ², where t* is the critical stressor layer thickness (inmicrons), K_(IC) is the fracture toughness (in units of MPa·m^(1/2)) ofthe base substrate 10 and σ is the stress value of the stressor layer(in MPa or megapascals). The above expression is a guide, in practice,spalling can occur at stress or thickness values up to 20% less thanthat predicted by the above expression.

Illustrative examples of materials that are under tensile stress whenapplied atop the base substrate 10 and thus can be used as the stressorlayer 16 include, but are not limited to, a metal, a polymer, such as aspall inducing tape layer, or any combination thereof. The stressorlayer 16 may comprise a single stressor layer, or a multilayeredstressor structure including at least two layers of different stressormaterial can be employed.

In one embodiment, the stressor layer 16 is a metal. In anotherembodiment, the stressor layer 16 is a spall inducing tape. In anotherembodiment, for example, the stressor layer 16 may comprise a two-partstressor layer including a lower part and an upper part. The upper partof the two-part stressor layer can be comprised of a spall inducing tapelayer.

When a metal is employed as the stressor layer 16, the metal caninclude, for example, Ni, Cr, Fe, or W. Alloys of these metals can alsobe employed. In one embodiment, the stressor layer 16 includes at leastone layer consisting of Ni.

When a polymer is employed as the stressor layer 16, the polymer is alarge macromolecule composed of repeating structural units. Thesesubunits are typically connected by covalent chemical bonds.Illustrative examples of polymers that can be employed as the stressorlayer 16 include, but are not limited to, polyimides polyesters,polyolefins, polyacrylates, polyurethane, polyvinyl acetate, andpolyvinyl chloride.

When a spall inducing tape layer is employed as the stressor layer 16,the spall inducing tape layer includes any pressure sensitive tape thatis flexible, soft, and stress free at a first temperature used to formthe tape, yet strong, ductile and tensile at a second temperature usedduring removal of the upper portion of the base substrate 10. By“pressure sensitive tape,” it is meant an adhesive tape that will stickwith application of pressure, without the need for solvent, heat, orwater for activation. Tensile stress in the tape at the secondtemperature is primarily due to thermal expansion mismatch between thebase substrate 10 (with a lower thermal coefficient of expansion) andthe tape (with a higher thermal expansion coefficient).

Typically, the pressure sensitive tape that is employed in the presentdisclosure as stressor layer 16 includes at least an adhesive layer anda base layer. Materials for the adhesive layer and the base layer of thepressure sensitive tape include polymeric materials such as, forexample, acrylics, polyesters, olefins, and vinyls, with or withoutsuitable plasticizers. Plasticizers are additives that can increase theplasticity of the polymeric material to which they are added.

In one embodiment, the stressor layer 16 employed in the presentdisclosure can be formed at a first temperature which is at roomtemperature (15° C.-40° C.). In another embodiment, when a tape layer isemployed, the tape layer can be formed at a first temperature which isfrom 15° C. to 60° C.

When the stressor layer 16 is a metal or polymer, the stressor layer 16can be formed utilizing deposition techniques that are well known tothose skilled in the art including, for example, dip coating,spin-coating, brush coating, sputtering, chemical vapor deposition,plasma enhanced chemical vapor deposition, chemical solution deposition,physical vapor deposition, and plating.

When the stressor layer 16 is a spall inducing tape layer, the tapelayer can be applied by hand or by mechanical means to the structure.The spall inducing tape can be formed utilizing techniques well known inthe art or they can be commercially purchased from any well knownadhesive tape manufacturer. Some examples of spall inducing tapes thatcan be used in the present disclosure as stressor layer 16 include, forexample, Nitto Denko 3193MS thermal release tape, Kapton KPT-1, andDiversified Biotech's CLEAR-170 (acrylic adhesive, vinyl base).

In one embodiment, a two-part stressor layer can be formed on a surfaceof the base substrate 10, wherein a lower part of the two-part stressorlayer is formed at a first temperature which is at room temperature orslight above (e.g., from 15° C. to 60° C.), wherein an upper part of thetwo-part stressor layer comprises a spall inducing tape layer at anauxiliary temperature which is at room temperature.

If the stressor layer 16 is of a metallic nature, it typically has athickness of from 3 μm to 50 μm, with a thickness of from 4 μm to 7 μmbeing more typical. Other thicknesses for the stressor layer 16 that arebelow and/or above the aforementioned thickness ranges can also beemployed in the present disclosure.

If the stressor layer 16 is of a polymeric nature, it typically has athickness of from 10 μm to 200 μm, with a thickness of from 50 μm to 100μm being more typical. Other thicknesses for the stressor layer 16 thatare below and/or above the aforementioned thickness ranges can also beemployed in the present disclosure.

Referring now to FIGS. 3A-3E, there are illustrated the structure ofFIG. 2 after forming a trench 20 within the spalling structure (i.e.,the base substrate 10, the optional metal-containing adhesion layer 14,the optional plating seed layer 15 and the stressor layer 16) usinglaser ablation. In some embodiments, the trench 20 is formed partiallywithin the stressor layer 16 (not shown). In another embodiment, thetrench 20 is formed completely through the stressor layer 16, but stopswithin or is formed completely through the optional plating seed layer15. In a further embodiment, the trench 20 is formed completely throughthe stressor layer 16, but stops within or is formed completely throughthe optional metal-containing adhesion layer 14. Other embodiments, someof which are illustrated in FIGS. 3A-3E, are also possible.

In the embodiment depicted in FIG. 3A, the trench 20 stops on anuppermost surface of the base substrate 12. In the embodiment depictedin FIG. 3B, the trench 20 extends in the base substrate 10 to a depththat is less than the fracture plane 18. In the embodiment depicted inFIG. 3C, the trench 20 extends in the base substrate 10 to a depth thatis equal to the fracture plane 18. In the embodiment depicted in FIG.3D, the trench 20 extends in the base substrate 10 to a depth that isgreater than the fracture plane 18. In the embodiment depicted in FIG.3E, the trench 20 extends in the base substrate 10 and has an expandedwidth opening 24. In FIGS. 3A-3E, the designation “L” refers to aportion of a specific material that will not be involved in subsequentspalling due to its being outside a boundary of a region to be spalled.The designation “R” refers to a portion of a specific material layerthat will be involved in spalling due to its being inside a boundary ofa region to be spalled. The stressor layer 16R can be referred to as astress concentration region of the spalling structure.

As shown, the trench 20 that is formed by laser ablation has a surfacewithin the trench on which spalling can be initiated. As such, fractureof the base substrate 10 begins on a trench surface and continues untilreaching a condition of controlled propagation along fracture plane 18.

Notwithstanding the depth of the trench 20, the trench is formed bylaser ablation. In some embodiments and as shown in FIG. 3E, a trenchformed by laser ablation may be expanded by other etch processes to formthe trench 20 with the expanded width opening 24. Expanded width opening24 would typically have interior corners 25 functioning as stressconcentration regions.

For the case of certain base substrates 10 (e.g., monocrystalline Siwith an appropriate orientation), the structure of FIG. 3E may be formedfrom the structure of FIG. 3D, using an anisotropic wet etch employing ahydroxide solution including at least one of KOH, NaOH, CeOH, RbOH,NH₄OH, or tetramethylammonium hydroxide (TMAH), or a wet etch employingethylene diamine pyrocatechol (EDP).

The laser ablation process (which can also be referred to herein aslaser scribing) preferably includes a pulsed irradiation process. Whilecontinuous wave (CW) lasers may, in certain circumstances, also be usedto define trench edges in a stressor layer stack, pulsed irradiation isgenerally preferable because material removal can be accomplished withsignificantly less heating outside the immediate area being irradiated.Optimal conditions will depend on the absorption characteristics andphysical properties of the material layers being ablated. In someembodiments in which both a polymeric stress inducing tape and ametal-containing stressor layer are employed, an ultraviolet (UV)wavelength laser (e.g., one with a wavelength in the range 193 nm to 355nm) can be used to ablate the stress inducing tape while a UV or longerwavelength laser (e.g., one with a wavelength in the range 193 nm to1064 nm) can be used to ablate the metal-containing stressor layer.Generally, the laser ablation can be performed at any wavelength atwhich the material to be ablated has (i) a high absorption coefficient α(or short absorption length 1/α), where 1/α is defined as the thicknessof material that will result in a 1/e attenuation in transmitted lightintensity, and (ii) a reflectivity that is compatible with at least somelight absorption. For example, Ni can be ablated well at both 532 nm and1064 nm. At a wavelength of 532 nm, Ni has a room temperature 1/α valueof about 10-13 nm and a reflectivity of about 60-65%, whereas at awavelength of 1064 nm Ni has a room temperature 1/α value of about 18 nmand a reflectivity of about 66-74%. Many semiconductors have absorptioncoefficients that strongly increase with temperature, thus allowingablation to occur even in materials that are only weakly absorbing atroom temperature.

A variety of pulsed lasers may be used to effect ablation, including,but not limited to, diode-pumped solid state (DPSS) lasers and excimerlasers, with pulse widths (or durations) ranging from the femtosecondrange to the microsecond range. In one embodiment a diode-pumpedQ-switched laser with an output at 1064 nm or 532 nm (e.g., a CoherentMATRIX-1064 or MATRIX-532) is used in an OpTek laser scribing systemwhich has a stationary laser and a moving sample stage. In otherembodiments, the laser beam can be moved while the sample is heldstationary. The laser ablation can be performed in a single pass, ormultiple passes can be used. When multiple passes are employed, from 2to 30 passes are typically, but not necessarily always, employed.Qualitatively, the number of passes required to ablate a trench in agiven material to a given depth is proportional to the scan speed (e.g.,two passes at a scan speed of 100 mm/sec produce approximately the sameeffect as one pass at 50 mm/sec). The number of passes to ablate a giventrench would typically be proportional to the desired trench depth (morepasses for deeper trenches) and inversely proportional to the amount ofmaterial ablated with each laser pulse.

In one embodiment, the laser ablation is performed at a scan rate ofabout 50 mm/sec-100 mm/sec with radiation focused to a spot size of 30μm-60 μm diameter using repetition rates from 30 kHz to 100 kHz, pulsewidths ranging from 20 ns to 40 ns, and an average power from 8 W to 15W. For a repetition rate of 50 kHz, pulse width of 30 ns, and averagepower of 15 W, these conditions correspond to a pulse energy of 300 μJ,a fluence per pulse of 11 J/cm²-42 J/cm², and a peak power of 3.5×10⁸W/cm² to 1.4×10⁹ W/cm². Other repetition rates, pulse widths, and pulseenergies can also be employed in forming the laser ablated trenches. Asa general rule, the fluence per pulse required for ablation decreases aspulse width decreases. Depending on the laser pulse width, metals can beablated at one of a fluence per pulse from 0.1 J/cm² to 200 J/cm² and apower density from 1×10⁸ W/cm² to 1×10¹⁴ W/cm².

Specifically, spontaneous spalling has been observed in base substratesof Si with adhesion/plating seed layers of Ti(50 nm)/Ni(400 nm) andplated Ni stressor layers of thickness 20 μm-30 μm after 3-4 passes withlaser conditions of wavelength 1064 nm, repetition rate 60 kHz, averagepower 15 W, and pulse width about 30 ns and scan conditions of 100mm/sec to form a trench about 40 μm wide. These conditions correspond toa pulse energy of 250 μJ, a fluence per pulse of about 20 J/cm² and apeak power density of 6.6×10⁸ W/cm². While in certain cases spontaneousspalling is desired, it is typically more preferably to form the laserablated trenches without spalling and to complete spalling with the useof an optional handle substrate.

The characteristics of the trench 20 formed, such as trench depth andamount of material build-up at the trench edges, can be varied byadjusting the laser focus and the duration of laser exposure. Samplescans speeds can range from 50 mm/s to 100 mm/s.

Trenches 20 can formed in any pattern or arrangement desired by theuser, including polygons and circles. FIGS. 14A-14D show top views ofsome exemplary shapes of the trenches 20 that can be formed laserablation. Specifically, FIG. 14A shows that the trenches can be in theshape of a square 100 and FIG. 14B shows that the trench can be in theshape of a circle 102. Such shapes are useful when one wants to makeclean stressor layer edges just inside the periphery of base substratescomprising square or round ingots. FIG. 14C shows that the trench can bein the shape of flexible interconnect nested rings 104, and FIG. 14Dshows that the trench can be in the shape of linked squares 106. Suchshapes might be useful for which especially thick stressor layers and/orspalled films make additional flexibility desirable.

Referring to FIG. 4, there is depicted the structure of FIG. 3A afterforming an optional handle substrate 26 atop stressor layer portion 16R.It is noted that although FIG. 3A is illustrated as including theoptional handle substrate 26, an optional handle substrate 26 can beformed atop any of the structures depicted in FIGS. 3B, 3C, 3D and 3E.

The optional handle substrate 26 employed in the present disclosurecomprises any flexible material which has a minimum radius of curvatureof less than 30 cm. Illustrative examples of flexible materials that canbe employed as the optional handle substrate 26 include a metal foil ora polyimide foil. The optional handle substrate 26 can be used toprovide better fracture control and more versatility in handling thespalled portion, i.e., the portion of the base substrate below stressorlayer portion 16R and above the fracture plane 18, of the base substrate10. Moreover, the optional handle substrate 26 can be used to guide thecrack propagation during spalling. The optional handle substrate 26 ofthe present disclosure is typically, but not necessarily, formed at afirst temperature which is at room temperature (15° C.-40° C.).

The optional handle substrate 26 can be formed utilizing depositiontechniques that are well known to those skilled in the art including,for example, dip coating, spin-coating, brush coating, sputtering,chemical vapor deposition, plasma enhanced chemical vapor deposition,chemical solution deposition, physical vapor deposition, and plating.The optional handle substrate 26 typical has a thickness of from 1 μm tofew mm, with a thickness of from 70 μm to 120 μm being more typical.Other thicknesses for the optional handle substrate 26 that are belowand/or above the aforementioned thickness ranges can also be employed inthe present disclosure.

Referring now to FIG. 5, there is depicted the structure of FIG. 4 afterremoving a material layer region 10′ of the base substrate 10 byspalling. Spalling can be initiated at room temperature or at atemperature that is less than room temperature. In one embodiment,spalling is performed at room temperature (i.e., 20° C. to 40° C.). Inanother embodiment, spalling is performed at a temperature less than 20°C. In a further embodiment, spalling occurs at a temperature of 77 K orless. In an even further embodiment, spalling occurs at a temperature ofless than 206 K. In still yet another embodiment, spalling occurs at atemperature from 175 K to 130 K.

When a temperature that is less than room temperature is used, the lessthan room temperature spalling process can be achieved by cooling thestructure down below room temperature utilizing any cooling means. Forexample, cooling can be achieved by placing the structure in a liquidnitrogen bath, a liquid helium bath, an ice bath, a dry ice bath, asupercritical fluid bath, or any cryogenic environment liquid or gas.

When spalling is performed at a temperature that is below roomtemperature, the spalled structure is returned to room temperature byallowing the spalled structure to slowly warm up to room temperature byallowing the same to stand at room temperature. Alternatively, thespalled structure can be heated up to room temperature utilizing anyheating means.

After spalling, the optional handle substrate 26, stressor layer portion16R, and, if present the optional plating seed layer portion 15R and theoptional metal-containing adhesion layer portion 14R can be removed fromthe material layer region 10′ of the base substrate 10. The unspalledbase substrate is labeled as 11. The stressor layer portions 16L and, ifpresent the optional plating seed layer portion 15L and the optionalmetal-containing adhesion layer portion 14L can be removed from theunspalled portion of the base substrate 11.

The optional handle substrate 26 and the stressor layer portion 16R andthe optional plating seed layer portion 15R and the optionalmetal-containing adhesion layer portion 14R can be removed from thematerial layer region 10′ of the base substrate utilizing conventionaltechniques well known to those skilled in the art. Portions 16L, 15L and14L can be removed from the unspalled portion of the base substrate 11utilizing similar well known processes. For example, and in oneembodiment, aqua regia (HNO₃/HCl) can be used for removing the optionalhandle substrate 26, the stressor layer portions 16R and 16L, theoptional plating seed layer portions 15R and 15L and the optionalmetal-containing adhesion layer 14R and 14L. In another example, UV orheat treatment is used to remove the optional handle substrate 26,followed by a chemical etch to remove the stressor layer portions 16Rand 16L, followed by a different chemical etch to remove the optionalplating seed layer portions 15R and 15L and optional metal-containingadhesion layer portions 14R and 14L.

The thickness of the material layer region 10′ of the base substrate 10varies depending on the material of the stressor layer 16 and thematerial of the base substrate 10 itself. In one embodiment, thematerial layer region 10′ of the base substrate 10 has a thickness ofless than 100 microns. In another embodiment, the material layer region10′ of the base substrate 10 has a thickness of less than 50 microns.

Reference is now made to FIGS. 6, 7, 8A-8B, 9 and 10 which illustrateanother embodiment of the present disclosure. In this embodiment, laserablation is used to form a trench within a blanket material stackincluding at least an uppermost plating seed layer. A stressor layer isformed on the laser ablated material stack and one portion of thestressor layer has a stress inducing edge that can be used for spalling.

This embodiment of the present disclosure begins by first providing abase substrate 10 such as shown in FIG. 1. After providing the basesubstrate 10, a material stack 52 including at least an upper platingseed layer is formed on the uppermost surface 12 of the base substrate10. In some embodiments, material stack 52 also includes ametal-containing adhesion layer beneath the plating seed layer. Thedescription of the metal-containing adhesion layer and plating seedlayer employed in this embodiment is the same as that described abovefor the optional metal-containing adhesion layer 14 and the optionalplating seed layer 15. As such, the above materials, thicknesses andprocesses of forming the optional metal-containing adhesion layer 14 andthe optional plating seed layer 15 can be used herein to describe suchlayers that can be present in the material stack 52. The structureincluding the material stack 52 on the uppermost surface 12 of the basesubstrate 10 is shown, for example, in FIG. 6.

Referring now to FIG. 7, there is illustrated the structure of FIG. 6after forming a trench 54 through at least some of material stack 52 and(as shown) optionally into a portion of the base substrate 10. If trench54 formed in this embodiment extends into the base substrate, it canhave a depth that is greater than the fracture plane, equal to thefracture plane, or less than the fracture plane. The fracture plane isnot yet defined in FIG. 7. The trench 54 is formed by laser ablation.The laser ablation process, conditions, and shapes used in formingtrench 20 in the previous embodiment can be used here for forming trench54. In FIG. 7, reference 52L denotes a portion of the material stackthat will not be involved in spalling, while reference numeral 52Rdenotes a portion of the material stack that will be involved insubsequent spalling.

Referring now to FIGS. 8A-8B, there are illustrated the structure ofFIG. 7 after forming a stressor layer portion (56R, 56L, 56M). In FIG.8A, the stressor layer portions 56L (portion not involved in spalling)and 52R (portion involved in spalling) are formed by selective plating,while in FIG. 8B the stressor layer portions (56R, 56L, and 56M) areformed by non-selective plating. The term “selective plating” as usedhere denotes that the stressor layer portions 56L and 56R are formedonly on the upper surfaces of material stack portions 52L and 52R,respectively. The term “non-selective plating” as used here thus denotesthat the stressor layer portions 56R, 56L, and 56M are formed on allexposed horizontal surfaces of the structure shown in FIG. 7. In thenon-selective embodiment in which stressor layer portion 56M is formedwithin the trench 54, stressor layer portion 56M acts as a crack stoplayer in the structure This functionality may have specialized uses incertain applications, but it is not expected to be desirable forspalling.

In the selective embodiment, the stressor layer portion 56M is absentand stressor layer portion 56R provides the stressor layer edge, asshown in FIGS. 8A-8B. Selective plating processes are well known in theart. As described by Y. S. Liu in U.S. Pat. No. 4,988,412, metals suchas Ni may be selectively plated on conductive seed layers comprising abottom layer of a material that Ni will not plate on (e.g., Al, or eventhe bare substrate itself) and a top layer of a material that Ni willplate on (e.g., Au or Ni). Regions of the top seed layer material areremoved to expose regions of the bottom seed layer material whereplating is not desired. In principle, it should be possible to get Ni toplate on a noble or near-noble metal seed layer selectively to exposedregions of a semiconductor base substrate (e.g., p-type Si). However, inpractice, it can be difficult to cleanly ablate regions of seed material52 without leaving residual metal-semiconductor compounds (e.g.,silicides) on which Ni will readily plate.

The stressor layer portions (56R and 56M) of this embodiment of thepresent disclosure comprise one of the metal-containing stressormaterials mentioned above for stressor layer 16.

Referring now to FIG. 9, there is illustrated the structure of FIG. 8Aafter forming an optional handle substrate 58 atop the stressor layerportion 56R. Although illustration is made to forming the optionalhandle substrate 58 to the structure shown in FIG. 8A, the optionalhandle substrate 58 can also be formed on the structure shown in FIG.8B. The material, thickness and process of forming the optional handlesubstrate 58 are the same as that mentioned above in the firstembodiment for the optional handle substrate 26.

Referring now to FIG. 10, there is illustrated the structure of FIG. 9after removing an upper portion 10 of the base substrate 10 by spalling.The spalling used in this embodiment is the same as the spallingdescribed above for the first embodiment.

Reference now is made to FIGS. 11-13 which illustrate a third embodimentof the present disclosure. In this embodiment, laser ablation is used toform a trench within an edge of the base substrate itself. Thelaser-defined trench has an edge that can be used for spalling.

This embodiment of the present disclosure begins by first providing thestructure that is illustrated in FIG. 2 of the first embodiment of thepresent disclosure. Although not illustrated, an optional plating seedlayer can be formed between the optional metal-containing adhesion layer14 and the stressor layer 16, or between the base substrate 10 and thestressor layer 16. In some embodiments, no optional metal-containingadhesion layer 14 and optional plating seed layer are employed. Forillustrative purposes only, the plating seed layer 15 of FIG. 2 will notbe shown in FIGS. 11-13.

Referring to FIG. 11, there is illustrated the spalling structure afterforming a laser-ablated trench 70 in a vertical sidewall of the basesubstrate 10. The laser ablation process, conditions, and shapes used informing trench 20 in the previous embodiment can be used here forforming laser-ablated trench 70. In this embodiment, the depth of trench70 can vary and also laser ablation can be used in conjunction with anetching process, for example an anisotropic etching process, to providea trench in the base substrate 10 that has an expanded width openingtherein.

Referring to FIG. 12, there is depicted the structure of FIG. 11 afterforming an optional handle substrate 72 atop the stressor layer 16. Thematerial, thickness and process of forming the optional handle substrate72 is the same as that mentioned above in the first embodiment for theoptional handle substrate 26.

Referring to FIG. 13, there is illustrated the structure of FIG. 12after removing a material layer region 10′ of the base substrate 10 byspalling. Spalling used in this embodiment is the same as that mentionedabove for the first embodiment of the present disclosure.

While the present disclosure has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present disclosure. It is therefore intended that the presentdisclosure not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

What is claimed is:
 1. A method of removing a material layer region of abase substrate, said method comprising: forming a material stackcomprising at least a plating seed layer atop an uppermost surface of abase substrate; forming a trench by laser ablation at least within thematerial stack to define an edge of a material layer region to bespalled; forming a stressor layer portion on a non-ablated portion ofthe material stack; and spalling the material layer region of the basesubstrate.
 2. The method of claim 1, wherein said material stack furtherincludes a metal-containing adhesion layer located beneath said platingseed layer.
 3. The method of claim 1, wherein said forming said stressorlayer portion comprises a selective plating process.
 4. The method ofclaim 1, wherein said stressor layer portion is a metal, a polymer orany combination thereof.
 5. The method of claim 4, wherein said stressorlayer portion includes at least said polymer, and said polymer is astress inducing tape layer.
 6. The method of claim 1, wherein said laserablation comprises pulsed irradiation performed at one of a fluence perpulse from 0.1 to 200 J/cm² and a power density from 1×10⁸ to 1×10¹⁴W/cm².
 7. The method of claim 1, wherein said trench has a shape of apolygon, circle, flexible interconnect nested rings or linked squares.8. The method of claim 1, wherein said spalling is performed at roomtemperature or a temperature less than room temperature.
 9. The methodof claim 1, further comprising forming a handle substrate atop saidstressor layer portion prior to spalling.
 10. A method of removing amaterial layer region of a base substrate, said method comprising:forming at least a stressor layer atop an uppermost surface of a basesubstrate; forming a trench by laser ablation within a vertical sidewallportion of the base substrate, said trench defining an edge of amaterial layer region of the base substrate to be spalled; and spallingthe material layer region of the base substrate.
 11. The method of claim10, further comprising at least one of a metal-containing adhesion layerand a plating seed layer located beneath said stressor layer.
 12. Themethod of claim 10, wherein said stressor layer is a metal, a polymer orany combination thereof.
 13. The method of claim 12, wherein saidstressor layer includes at least said polymer, and said polymer is astress inducing tape layer.
 14. The method of claim 10, wherein saidspalling is performed at room temperature or a temperature less thanroom temperature.
 15. The method of claim 10, further comprising forminga handle substrate atop said stressor layer portion prior to spalling.